1. Field of the Invention
This invention relates to circuit breakers for protecting electric power circuits and, more particularly, to remotely controllable circuit breakers including a set of secondary contacts, which can be remotely controlled.
2. Background Information
Circuit breakers used in residential and light commercial applications are commonly referred to as miniature circuit breakers because of their limited size. Such circuit breakers typically have a set of separable contacts opened and closed by a spring powered operating mechanism. A thermal-magnetic trip device actuates the operating mechanism to open the separable contacts in response to persistent overcurrent conditions and to short circuit conditions.
Usually, circuit breakers of this type for multiple circuits within a residence or commercial structure are mounted together within a load center, which may be located in a basement or other remote location. In some applications, it has been found convenient to use the circuit breakers for purposes other than just protection, for instance, for load shedding. It is desirable to be able to perform this function remotely, and even automatically, such as with a computer.
When a remotely controlled set of contacts, such as a set of secondary contacts, are in series with a circuit breaker, such as one having a set of main contacts, at certain voltage and current values it is necessary to control the blow off of the former contacts during short circuit conditions. For example, U.S. Pat. No. 6,259,339 discloses that in order for the set of secondary contacts to withstand short circuit currents and allow the set of main contacts to perform the circuit interruption, the magnet force generated by the short circuit current causes a movable armature mounted on a secondary contact arm to be attracted to a fixed pole piece seated in a molded housing, thereby clamping the secondary contacts closed.
There is room for improvement in circuit breakers and in remotely controllable circuit breakers employing a set of secondary contacts.
These needs and others are met by the present invention, which provides improvements in controlling the blow off of a set of secondary contacts during certain fault conditions, such as a short circuit condition.
In accordance with the invention, first and second magnetic armatures respond to a first predetermined condition of current flowing through a first circuit, which electrically connects a set of first contacts to a set of second contacts. These armatures cooperate to hold such set of second contacts in a closed state during such first predetermined condition of current. Furthermore, the first and second magnetic armatures respond to a second predetermined condition of current flowing in a second circuit, which electrically connects an arc plate associated with the set of first contacts and a second or load terminal. The armatures cooperate to hold such set of second contacts in the closed state during such second predetermined condition of current. In this manner, the first and second magnetic armatures respond through the first circuit to prevent blow off of the set of second contacts during initial fault or short circuit conditions, and the second circuit continues to prevent such blow off as the set of first contacts is opened by causing arcing current to be diverted from the arc plate and through the second circuit.
As one aspect of the invention, a circuit breaker comprises: a housing; a first terminal; a second terminal; a set of first contacts mounted in the housing; an operating mechanism mounted in the housing and coupled to the set of first contacts for opening and closing the set of first contacts; an arc plate drawing an arc from one of the first contacts when the operating mechanism opens the set of first contacts; a set of second contacts mounted in the housing, the set of second contacts having an open state and a closed state, and being electrically interconnected with the set of first contacts between the first and second terminals; a first circuit electrically connecting the set of first contacts to the set of second contacts; an actuator mounted in the housing, the actuator selectively moving the set of second contacts between the open and closed states; a second circuit electrically connected between the arc plate and the second terminal; a first magnetic armature coupled to the actuator; and a second magnetic armature, with the first and second circuits passing between the first and second magnetic armatures, the first magnetic armature and the second magnetic armature responsive to a first predetermined condition of current flowing in the first circuit and cooperating to hold the set of second contacts in the closed state during the first predetermined condition of current flowing in the first circuit, the first magnetic armature and the second magnetic armature responsive to a second predetermined condition of current flowing in the second circuit and cooperating to hold the set of second contacts in the closed state during the second predetermined condition of current flowing in the second circuit.
The first circuit may comprise a U-shaped conductor including a first leg electrically interconnected with the set of first contacts and a second leg electrically interconnected with the set of second contacts, with one of the first and second legs passing between the first and second magnetic armatures.
The set of first contacts may comprise a fixed contact electrically connected to the first terminal and a movable contact, the operating mechanism may comprise a movable arm carrying the movable contact, and the arc plate may draw the arc from the fixed contact when the movable arm opens the set of first contacts.
The movable arm may be a first movable arm, the fixed contact may be a first fixed contact, the movable contact may be a first movable contact, the set of second contacts may include a second fixed contact and a second movable contact, the actuator may comprise a second movable arm carrying the second movable contact, the first circuit may comprise a first flexible conductor electrically connected to the first movable arm, an intermediate conductor electrically connected to the first flexible conductor, and a second flexible conductor electrically connected between the intermediate conductor and the second movable arm. The second flexible conductor may pass from the intermediate conductor and between the first and second magnetic armatures before being electrically connected to the second movable arm.
The movable arm may be a first movable arm, the fixed contact may be a first fixed contact, the movable contact may be a first movable contact, the set of second contacts may include a second fixed contact and a second movable contact, the actuator may comprise a second movable arm carrying the second movable contact, and the first circuit may comprise at least one conductor electrically connected between the first movable arm and the second movable arm. One of the at least one conductor may be a flexible conductor, which passes between the first and second magnetic armatures before being electrically connected to the second movable arm. The first circuit may comprise a flexible conductor, which is electrically interconnected with the first movable arm, and a U-shaped conductor including a first leg electrically connected to the flexible conductor and a second leg electrically interconnected with the second movable arm, with one of the first and second legs passing between the first and second magnetic armatures.
As another aspect of the invention, a remotely controllable circuit breaker comprises: a housing; a first terminal; a second terminal; a set of first contacts mounted in the housing; an operating mechanism mounted in the housing and coupled to the set of first contacts for opening and closing the set of first contacts; an arc plate drawing an arc from one of the first contacts when the operating mechanism opens the set of first contacts; a set of second contacts mounted in the housing, the set of second contacts having an open state and a closed state, and being electrically interconnected with the set of first contacts between the first and second terminals; a first circuit electrically connecting the set of first contacts to the set of second contacts; a remotely controllable solenoid including a member coupled to the set of second contacts, the member movable to a first position in which the set of second contacts is in the open state and a second position in which the set of second contacts is in the closed state; a second circuit electrically connected between the arc plate and the second terminal; a first magnetic armature coupled to the member, and a second magnetic armature, the first and second circuits passing between the first and second magnetic armatures, the first magnetic armature and the second magnetic armature responsive to a first predetermined condition of current flowing in the first circuit and cooperating to hold the set of second contacts in the closed state during the first predetermined condition of current flowing in the first circuit, the first magnetic armature and the second magnetic armature responsive to a second predetermined condition of current flowing in the second circuit and cooperating to hold the set of second contacts in the closed state during the second predetermined condition of current flowing in the second circuit.
The second circuit may comprise a first conductor and a second flexible conductor, the second flexible conductor being electrically connected between the arc plate and the first conductor, the first conductor being electrically connected to the second terminal.
As another aspect of the invention, a circuit breaker comprises: a housing; a first terminal; a second terminal; a set of first contacts mounted in the housing; an operating mechanism mounted in the housing and coupled to the set of first contacts for opening and closing the set of first contacts; a set of second contacts mounted in the housing, the set of second contacts having an open state and a closed state, and being electrically interconnected with the set of first contacts between the first and second terminals; a circuit electrically connecting the set of first contacts to the set of second contacts; an actuator mounted in the housing, the actuator selectively moving the set of second contacts between the open and closed states; a first magnetic armature coupled to the actuator; and a second magnetic armature, with the circuit passing between the first and second magnetic armatures for at least two turns, the first magnetic armature and the second magnetic armature responsive to a predetermined condition of current flowing in the circuit and cooperating to hold the set of second contacts in the closed state during the predetermined condition of current flowing in the circuit.